1. Field of the Invention
This invention relates to a socket connector of the pin-and-socket type. When such a socket connector is unmated with a corresponding pin connector, it is susceptible to the undesired entry thereinto of electric currents resulting from the discharge of electrostatic charge that has accumulated on a human being or on a piece of apparatus which contacts or approaches the mating face of the socket connector. If such a discharge reaches any of the female connector contacts within the socket connector, the result can be a transient current from that connector contact or those connector contacts into circuitry conductively connected to the socket connector. If such circuitry includes certain types of solid-state devices, the devices may themselves be damaged by the transient current. Alternatively, data stored in solid-state memory chips may be lost or corrupted. Still further, if the socket connector is coupled to a telephone link or other communications circuit, it is possible for thousands of voice calls to be interrupted by spikes of undesirable noise caused by the transient current.
A most common source of electrostatic charge which might, unless prevented, discharge to one of the female connector contacts of the socket connector is the person holding or touching the socket connector. In the course of normal motions and activities such as scuffing shoes on a rug, a person can accumulate a charge at a voltage as high as 20,000 volts. This charge is developed by the process of frictional contact between unlike surfaces, sometimes called "triboelectric charging." Often, this triboelectric charge leaks away without the person even being aware that he or she has been charged and discharged. Sometimes, however, especially when the air is very dry, a person becomes distinctly aware that he is a charge carrier when a spark is drawn as he approaches a door knob or other metallic object to take hold of it.
Such a spark is a matter of extreme concern in the protection and handling of dataprocessing and communications equipment, especially if valuable data are stored therein or if valuable messages are being transmitted therethrough. Even if there is no perceptible spark, the amount of charge transmitted to and discharged through a socket connector by a person can be sufficient to cause damage. One particular time when such damage is especially likely is when a pin connector is being maneuvered toward the socket connector for the purpose of mating the two portions of the connector. Before the mating step is complete, a discharge may take place between one or more pins of the pin connector and one or more of the female connector contacts of the socket connector. Unless prevented, this discharge may take place even though the female connector contacts are recessed behind the mating face of the socket connector, and even though the body of that connector is made of an insulative material. If no structural modifications of the socket connector are made, a damaging discharge may take place despite careful precautions on the part of the person mating the two portions of the connector. That is to say, even though the person takes pains to "discharge himself" before he picks up the two members of the connector to mate them, the two members may nevertheless be at substantially different electric potentials and may draw a harmful spark before they are fully mated.
2. Description of the Prior Art
In the past, special precautions have been taken in the design of modem interface connectors in order to protect electronic equipment conductively coupled to one or more members of the respective interface connectors. In some cases, electrical filter components have been built into each contact of each member of each interface connector. However, this approach has been so expensive as to be impractical. Moreover, the space available within multi-pin connectors is not sufficient to accommodate filter components capable of significantly improving the safety performance of such interface connectors.
Another approach which is more practical and which has significantly improved safety performance is that which is described in U.S. Pat. No. 4,824,377, issued to Agostino L. DeBurro on Apr. 25, 1989. That patent discloses a socket connector in which the mating face incorporates a conductive sheet or a wire which surrounds the passageways in the face of the connector through which the pins of the pin connector must pass in order to mate with the respective female connector contacts having proximate ends set back slightly from the face of the socket connector. The conductive sheet or wire is connected to the metallic shell of the socket connector, which is in turn grounded so as to drain away any charge that may jump from the pins of the pin connector to the conductive sheet or wire. The connector in accordance with the DeBurro patent represented a substantial step forward, but the precise placement of the conductive sheet or wire on the face of the connector was an expensive operation.